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Troubleshooting electrical wiring after a smoked PMD

Tinker

Tinker

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Location
Lavonia, Georgia
I had nearly the same symptoms as detailed in this thread: https://www.thetruckstop.us/forum/threads/smoking-pmd.48938/

Engine ran away, wouldn't respond to throttle input. Smoke and burning smell from the PMD. 4-year history of occasional stalls with immediate restarts and also fishbiting under load (like going uphill).

I did all of the normal troubleshooting (followed the guide at Accurate Diesel) and each point seemed to checked out well enough. The thread referenced above has been very helpful. All roads seem to lead to either electrical or IP or both.

I've pulled the valley harness and checked the continuity on all wires leading to the PMD and optical sensor. No shorts in testing, no notable damage (one pinhead sized nick in a fairly safe area that I'll wrap up). I have a hard time believing this is just an R2 of the IP but that seems the logical next step. I just thought I'd post this to see if there are other ideas before I spend for the IP.

Is there anything else I can check in the harness? Any other potential source of shorting? Any alternative reason a PMD would get so hot it starts smoking? It was in the original location, but I'm thinking something sudden that led to catastrophic failure.

Prior to pulling the intake apart, I had tried multiple PMDs including brand new ones with no result so I'm reasonably confident it's not just the PMD.

Thanks so much for your help.
 
The IP harness can go bad even if it is tested good.
You cannot test it while the engine is running.
IMO, I will replace that IP harness since you are already there.

Where is the location of PMD when it smokes?
What is the fuel level when it happened? Low fuel can cause PMD to overheat also.
How big is the heatsink if it is relocated?
 
JMJNet said:
The IP harness can go bad even if it is tested good.
You cannot test it while the engine is running.
IMO, I will replace that IP harness since you are already there.

Where is the location of PMD when it smokes?
What is the fuel level when it happened? Low fuel can cause PMD to overheat also.
How big is the heatsink if it is relocated?
Click to expand...
PMD was in the original location when it went up in smoke. Clearly overheated but I'm wondering if there is some other failure mode besides electrical shorting that could cause it to get that hot. Fuel level was definitely 1/4 tank or less, don't remember exactly. But you seem to be heading down the path I was thinking - low fuel flow (for whatever reason) might have caused a sudden overheat.

If that's not reasonable, then I probably need to keep looking for other possible sources of too much current. At least that's what I'm thinking.

Thanks for your questions and ideas.
 
Rockabillyrat said:
Sounds to me like the fuel solenoid on the injection pump is bad and took out the PMD.
Click to expand...
Checking the fuel shutoff solenoid was in the troubleshooting guide I used and I pulled it out and tested it to 12v. It plunged properly.

One thing that doesn't make sense about the low fuel flow explanation is that the engine ran away at first. Not a full throttle runaway, but it wanted to take me from the 55ish I was traveling up to 65-70mph with no throttle response, though I could control it with the cruise control engaged. After I went to N and pulled over, it ran really rough. But that was also about the time the PMD started smoking.
 
iirc worn plunger inside ip creates more load drawing really high amps from the pmd drivers (the 2 metal cans you see in it).
 
Will L. said:
iirc worn plunger inside ip creates more load drawing really high amps from the pmd drivers (the 2 metal cans you see in it).
Click to expand...
Okay, so you and Rockabillyrat are talking about the internal fuel solenoid? That is the one that received the signals from the PMD via the red and black wires under the boot, right? I don't know much about the magic that happens inside the IP. Automatically assumed he was talking about the shutoff solenoid.

That's very helpful. Thanks for clarifying.
 
Wills talking about the pmd drivers. Pop the cap off of the pmd and you'll see them in there
 
Jaryd said:
Wills talking about the pmd drivers. Pop the cap off of the pmd and you'll see them in there
Click to expand...
Thanks. I was referring to his comment about the plunger. I had an aha! moment when I realized he and Rockabillyrat were talking about the internal fuel solenoid possibly frying the PMD drivers; not the shutoff solenoid, which is what I originally thought they meant.
 
Rockabilly was talking about the exterior fuel shut off solenoid. I am talking about the internal magical pixie parts.

definitely exhaust all exterior options first.
 
JMJNet said:
The IP harness can go bad even if it is tested good.
You cannot test it while the engine is running.
IMO, I will replace that IP harness since you are already there.

Where is the location of PMD when it smokes?
What is the fuel level when it happened? Low fuel can cause PMD to overheat also.
How big is the heatsink if it is relocated?
Click to expand...

@JMJNet , do you have a source for the harnesses? I checked Quadstar (referenced in the other thread that addresses smoked PMD) but they're sold out of their "over-the-intake" harness. GM doesn't carry, apparently. No hits on any of my normal go-to parts sites either.

I did find someone building new ones and selling on ebay. Anyone have experience with Hotwire Innovations?
 
So your IP is maybe toast... It's time to seriously consider a DB2 IP conversion and eliminate the poor hellfire hot electronics GM shoved in the engine valley. Bad power wasting hot running design from the word go.

Looks like parts like the wiring harness for both are rare anymore.

IF a DB2 will start it will run till it 1) Runs out of Fuel. 2) Suffers a extreme failure that won't start again without new parts. The DS4 can stop running for a number of reasons just to piss you off.
 
WarWagon said:
So your IP is maybe toast... It's time to seriously consider a DB2 IP conversion and eliminate the poor hellfire hot electronics GM shoved in the engine valley. Bad power wasting hot running design from the word go.

Looks like parts like the wiring harness for both are rare anymore.

IF a DB2 will start it will run till it 1) Runs out of Fuel. 2) Suffers a extreme failure that won't start again without new parts. The DS4 can stop running for a number of reasons just to piss you off.
Click to expand...

I hear you. I read through the DB2 Conversion Guide by Bobbie Martin this afternoon. Definitely giving it some thought. But, at the moment, I'm thinking plug and play sounds better than making this a hobby vehicle.
 
I saw that harness on ebay sometimes.
It is supposed to come with the Stanadyne Gray PMD but some seller did not include it in their sale and sell it separately.

This one sells it with Gray PMD (at least in the picture, you may want to confirm it or check with the seller to see how much just for the harness):
www.ebay.com

NEW Stanadyne 39405 6.5l Pump Mounted Driver PMD FSD GM Chevy Turbo Diesel Fuel | eBay

This is the newest "bulletproof" version of this pmd.
www.ebay.com
 
Tinker said:
I hear you. I read through the DB2 Conversion Guide by Bobbie Martin this afternoon. Definitely giving it some thought. But, at the moment, I'm thinking plug and play sounds better than making this a hobby vehicle.
Click to expand...

I believe it's easier than his old guide today. You now have stand alone trans controllers and a 1993 cruise control unit that can make this conversion easy button. If the IP is toast the DB2 cost is near the same.

Back to your actual problem... You smoked the PMD. What exactly is wrong with the wiring harness? IMO it's fine with the short being in the IP like the last one that went out like this. However you are looking at it and can clear this up better. Just trying for you to not throw unneeded parts at it.

Make sure you get a NEW IP not a worn out rebuild from a shady company. It simply gets "old" to swap worn IP's out over and over. Done that myself enough to serve as a bad example.
 
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